Can you post or point to a picture? Maybe I should still try to build that Auditorium 23 SoloVox knock off for the 604 and see what happens (sonically).

Regards,

Chris

From the Onken thread ...

Quote:

Originally posted by IslandPink
"It would be interesting to combine the 45-degree slant edges of the HF Olson RCA LC-1A speaker with the double-wall Onken vents. This would substantially lower diffraction and retain the double-wall lossy vents of the Onken. Another clever variation would be to have different thicknesses of cabinet wall for the inner and outer surface, which would stagger the wall resonances, and make acoustic coupling from one to another less efficient."

As for the Audax ... um, well, I heard them a long time ago, back in the late 70's, and I thought they were reasonably good drivers that didn't require a lot of equalization. As I recall, they had very short Xmax, and were essentially midranges requiring a 200~300 Hz crossover for satisfactory performance.

In terms of smoothness and freedom from resonance, the Vifa 5.5" drivers in the Ariel are significantly flatter, have an extremely well-behaved rolloff region, and very rapid decay characteristics. But the efficiency is nearly 10 dB less, not a small difference. And using drivers in arrays does NOT give the same performance as a single, higher-efficiency driver. Just hassling with a pair of drivers added many months of hassle to the Ariel project - and that was with drivers that are as close to technically perfect as anything I've ever used. The prospect of using 2 or 4 drivers that are rougher, and have more pronounced breakups in the 3~10 kHz region, is very unappealing. The current fashion is brute-force 24 dB/octave crossovers (or ignoring the coloration), but I don't want to go down that path.

I tend to have strong go/no-go reactions to drivers. If I hear something special - an especially lyrical midrange, HF, or bass (in that order), I take note and try to find out what's going on that makes it special. I basically discount other people's opinions - sorry, no offense to anyone here - unless I know them and their taste personally. So I give weight to Gary Pimm, John Atwood, and Alexander, although I think Alex and I have different tastes in the midrange.

I haven't heard the new Jean Hiraga 604 Duplex, for example. The last time I heard a traditional 604, the midrange was one of the most colored and aggressive-sounding I ever heard, so the magnitude of the task facing Mr. Hiraga was enormous. On the other hand, he is one of the most experienced audio designers in the world, and has excellent tastes musically - so if anyone could pull off the near-impossible, it would be him. I wouldn't even attempt what he's done.

Sometimes I wonder why anyone listens to me. I'm a pretty lazy designer, and try and use the most linear devices I can find (flattest response, least energy storage, etc.) so I can concoct something around that. I kind of admire folks who visualize a Platonic Ideal of a loudspeaker, and work from the top down to bring the realization to the physical world. I just look for the prettiest pebbles on the beach, and make something around them.

There are some pix in the Issue 20 article of Positive Feedback magazine. Dave Robinson, the editor, lets me get away with an over-the-top style - so it ended up as a mashup of film noir, science fiction, and audio. Portland still looks a lot like the 1936 pix, by the way - just add water glistening on wet pavement, and the Chandler mood is already set. (Many inside jokes for the entertainment of the Portland Triode Society - all the locations are real.)

The last I saw of Gary's system (a couple of years ago), the mids were in open-ended boxes filled with Bonded Logic Ultratouch insulation, made from recycled blue jeans. This stuff has none of the scratchiness of fiberglass, and has very good broadband acoustic absorption. Think of a 1-cubic-foot wedge of the stuff in the mid and bass enclosures, and you get the picture. He also used a lot of rope caulk to quiet down the stamped-metal frames of the Beta 8's.

The crossovers are low-Q, low-order passive networks between the ribbon tweeters and the Beta 8's, and active Behringer lowpass for the damped-dipole W-baffles for the subwoofers. The subs use pairs of 15" drivers for each channel, and the heavily-modified Behringer is kept out of the mid/high signal path - all it does is EQ the woofs for the room and roll them off before the W-baffle goes into its first mode.

Another great thing about Bonded Logic is the price. Since it is marketed to home builders its very reasonably priced unlike the "special" audio grade stuff. I agree that the ST and NRC numbers for the material are excellent. I will look up the issue after I go home. Long day today,

I really like this picture - it's astonishing that downtown Portland still looks so much like this. Entirely appropriate to the 1935 vintage of the Western Electric 300A/B and the WE 86 and 92 amplifiers with Class A PP and Harmonic Balancer topologies. It's a good question which amplifier the "Liberty Theatre" used - the 92, 86, 43, RCA, or maybe it was a burlesque theatre. Probably not the latter - Broadway was the main street back then, and still is today.

The image quality of the Speed Graphic that was probably used for this picture had nothing to apologize for, either. The 16 x 20 print from the Oregon Historical Society that I scanned for this pix looks really good.

There are, but I'm not at liberty to share the data. I can report the measurements in the time and frequency domains for the Azurahorn AH425 and Altec/GPA 288 compression driver look very, very good. As reported elsewhere, the T=0.707 JMMLC horn is nowhere close to constant-directivity, but on the other hand, the data shows that it requires little to no equalization. Since I've been planning on using a supertweeter all along, the absence of CD is not a major concern. I'm still not 100% sold on the subjective qualities of CD horns, but that's a matter of personal taste.

I've been reflecting about what I want to accomplish, and the primary focus, more than ever, is minimum stored energy (combined with generous headroom). In measurements, stored energy appears as the "clutter" that appears after the initial impulse, or the extended ridges that appear in a CSD measurement. The AH425 & 288 are in the right ballpark from the preliminary data I've seen, and the first subjective reports.

I am working on a novel enclosure that is transitional between a "pure" dipole open-baffle and Gary Pimm's quasi-cardioid cotton-filled boxes with the rear panel open. That boxes store energy is well known - but classical dipoles also have the backwave diffract around to the front after a 1~2 mSec delay. This is also undesirable, although not as bad as the extended resonant signature of a closed box. I'm experimenting with lossy structures that aim for moderate (6~12 dB) attenuation of the backwave while avoiding mass-coupling effects on the midbass driver (which degrades efficiency, HF response, and transient response).

The Great Plains Audio Alnico 414's look like keepers - I'm now deciding between using a single or a pair per side. The pair has the charm of 101 dB/metre efficiency, and more headroom. Early tests indicate the AH425/288 works well all the way down to 600 Hz, so that gives more flexibility in the choice of the midbass drivers.

Healthwise, it's a matter of gradual improvement. I now have a personal trainer and work out at the gym three times a week - the goal is to improve symmetry of the muscles, and improve walking and running (which I was able to do for the first time a few weeks ago), and going up and down stairs with better safety. It's true, just like audio, the last 10% takes 90% of the work, time, and effort.